From the state of the art several jaw assemblies for/of surgical tubular shaft instruments are known. In the European patent application EP 1 712 187 A2, for example, a jaw assembly is illustrated in which the two arms/yaws are resiliently connected by means of a joint basis. In the area of their distal ends that are provided for holding and compressing the surgical clip and in this way applying the clip, each of the two arms includes a sliding surface on its outside. In order to close the jaw assembly and thus to apply the clip the jaw assembly is shifted relative to the shaft in which it is arranged in the proximal direction (the jaw assembly is thus partly pulled into the shaft and, resp., the shaft is slid over the jaw assembly) and the distal edge of the shaft slides off the sliding surfaces. The inclination of the sliding surfaces relative to the axis of the shaft causes the distal ends of the arms to be urged inwardly, while the proximal ends of the arms are held by the basis. In this way, each of the arms performs a rotation about the point at which the arms are connected to the basis. An opening operation of the jaw assembly takes moreover place unguided and is ensured exclusively by the elasticity of the arms urging back into their home position when the jaw assembly is slid out of the shaft during the opening operation.
A comparable jaw is also illustrated in the international patent application WO 2008/127 968, even if the instrument illustrated there is in total strongly different from the afore-described instrument.
The rotation of the arms during opening and closing the jaw assembly is resulting even more clearly from the US patent application US 2005/0171560 A1. There the distal areas of both arms are articulated at the basis and rotate about the mounting point. In this design, too, the clip is applied by the distal edge of the shaft sliding off the sliding surfaces provided on the outsides of the arms and in this way urging the arms inwardly.
The problem of this type of jaw assemblies resides in the fact that they have always the same closing geometry, more exactly speaking that in each case first the distal ends of the arms contact each other and pass by each other and thereafter follows the contact or the bypassing of the further proximally located areas of the arms. In the case of clip appliers this means that the clip is closed in each case from the distal end. For this reason, this structure of a jaw assembly is not useful to other surgical instruments such as, for example, endoscopic scissors.
It is another problem of jaw assemblies of this type that the opening of the jaw assembly is realized solely by the elasticity of the arms. The opening movement of the jaw is carried out unguided. Should a piece of tissue or any other part get between the front edge of the shaft and an arm of the jaw, this might obstruct the opening operation of the jaw assembly. Then the instrument would first have to be removed from the cavity inside the patient so as to be freed from the tissue piece and would subsequently have to be introduced into the patient again. This entails delays and troubles in the operating cycle.